Large-scale implementation of evidence-based psychotherapies (EBPs) such as Cognitive Processing Therapy (CPT) for Post-traumatic Stress Disorder can have a tremendous impact on mental and physical health, healthcare utilization, and quality of life. While many mental health systems have invested heavily in programs to implement EBPs, recent research has revealed a number of challenges to long-term sustainability and high- quality provision of these treatments. Few eligible patients receive EBPs in routine care settings, and clinicians do not appear to deliver the full treatment protocol to many of their patients. Emerging evidence suggest that when CPT and other EBPs are delivered at low levels of fidelity, clinical outcomes are negatively impacted. Clinicians have identified a number of reasons that they do not deliver EBPs that are related to the fit between the EBP and their patients or the clinical setting. To date, there is a dearth of guidance on how best to support and sustain high-quality EBP delivery. While some systems have policies and programs in place to support EBP implementation at the organization level, little is known about how to address remaining barriers that have been identified by clinicians. Identifying strategies to improve and sustain the delivery of CPT and other EBPs is therefore critical. Two competing strategies have been suggested in the existing literature. One emphasizes fidelity to the treatment protocol through ongoing consultation and fidelity monitoring. The other focuses on improving the fit and effectiveness of these treatments by making appropriate adaptations to the treatment or the clinical setting through a process of data-driven, continuous quality improvement. Neither has been evaluated in terms of impact on sustained implementation. To compare these approaches on key sustainability outcomes and provide some of the first guidance on strategies to promote sustainment, we propose a cluster randomized trial with mental health clinics (n=32) in three diverse mental health systems that have implemented CPT. Cohorts of clinicians and clinical managers will participate in one year of a fidelity oriented consultation or one year of a continuous quality improvement-oriented learning collaborative. Patient-level PTSD symptom change, fidelity and adaptation of CPT, penetration, and clinics' capacity to deliver EBP will be examined. Survey and interview data will also be collected to investigate multilevel influences on the success of the two implementation strategies. This research will be conducted by a team of investigators with expertise in CPT implementation, mixed-methods research strategies, quality improvement, and implementation science, with input from stakeholders in each participating mental health system. It will have broad implications for supporting ongoing delivery of EBPs in mental health and healthcare systems and settings. The resulting products have the potential to significantly improve efforts to ensure ongoing high quality implementation and consumer access to EBPs.